This invention concerns a method for controlling the warp let-off and cloth take-up motions on weaving machines, and in particular a method of processing the associated control signals so that they are not affected by the weaving pattern.
As is well known, textile quality depends to a large extent on the tension and speed of motion of the warp threads during weaving. The speed of the warp threads depends on the speed of motion of the cloth, which in turn depends on the operating speed of the weaving machine. As explained in the Belgian patent publication No. 768,521, the difference between the speed of the warp threads and the cloth respectively is dependent on the interweaving. Normally, all measures are taken to control the warp thread speed so that the tension in the warp threads is kept as close to a constant as possible. In BE No. 768,521, the instantaneous tension is measured and used to control the warp let-off. Likewise, in BE No. 768,521, the instantaneous speed of the weaving machine drive motor is measured and used to control the warp let-off.
Also in BE No. 768,521, the speed of the cloth take-up is directly determined from the speed of the main drive motor.
However, this method of operation has the disadvantage that the control system reacts to all disturbance signals, even though compensation is not necessary for disturbance signals of very short duration since these tend to be self-compensating. If a compensation function is nevertheless generated, there is a risk of overcompensation, with all the attendant disadvantages for the quality of the textile. The primary disturbance signals for which the control system does not need to provide compensation are the periodic variations in warp tension and machine speed caused by the weaving pattern.
The object of this invention is to provide a method for systematically avoiding these disadvantages. The method used in this invention primarily consists of: detecting the variation with respect to time of one or more of the operative parameters which are functionally related to the warp tension and/or warp speed; taking the signal thus obtained and removing those components of the signal which are due to variations in the weaving pattern and; using the resulting clean signal to control the warp let-off and/or cloth take-up.
Since the variations caused by the weaving pattern are always periodic, it is better not to feed them through to the warp drive, warp let-off or cloth take-up if the abovementioned disadvantages are to be avoided.
There are various processes by which the method of the invention can be applied, either by filtering out a number of disturbance signals or by processing the signal in one or more stages in order to provide a value which is representative of the signal over a duration equal to the period necessary for the formation of a complete weave pattern or a multiple thereof. Suitable processes include integration or determining the average of the signal over the relevant period.